use num::Num; // 0.2.0
use std::ops::{Sub, Mul};
use std::cmp::Eq;

fn fact<T>(n: T) -> T
    where T: Clone + Eq + Mul<T, Output = T> + Sub<T, Output = T> + Num
{
    if n == T::zero() {
        T::one()
    } else {
        fact(n.clone() - T::one()) * n
    }
}

fn main() {
    let x: u8 = 5;
    println!("{}", fact(x));

    let x: u16 = 5;
    println!("{}", fact(x));

    let x: u32 = 5;
    println!("{}", fact(x));

    let x: u64 = 5;
    println!("{}", fact(x));

    let x: u128 = 5;
    println!("{}", fact(x));
}